Thermally responsive viscosifiers in subterranean operations

ABSTRACT

Methods for the use of treatment fluids that include thermally responsive viscosifiers in subterranean formations are provided. In one embodiment, the methods include introducing a treatment fluid including an aqueous base fluid and a thermally responsive hydrogel including at least one thermoresponsive polymer into at least a portion of a subterranean formation; allowing the thermally responsive hydrogel to reach a thickening transition temperature, wherein the thermally responsive hydrogel undergoes a liquid-to-solid phase change at or above the thickening transition temperature; and allowing the treatment fluid to at least partially solidify in the subterranean formation, wherein the solid thermally responsive hydrogel is present in the treatment fluid in an amount from about 0.01 to about 0.2 by volume fraction of solids of the treatment fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to co-pending U.S. application Ser.No. 16/710,399 filed on Dec. 11, 2019, entitled “Thermally ResponsiveAnti-Sag Agents,” and U.S. application Ser. No. 16/710,342 filed on Dec.11, 2019, entitled “Thermally Responsive Lost Circulation Materials,”which granted on Mar. 30, 2021 as U.S. Pat. No. 10,961,431, both ofwhich are filed concurrently herewith, the entire disclosures of whichare incorporated herein by reference.

BACKGROUND

The present disclosure relates to methods for treating subterraneanformations, and to methods for using treatment fluids that includecertain viscosifiers in subterranean formations.

Treatment fluids often contain additives to impart desired physicaland/or chemical characteristics to the fluid. Such additives may includeviscosifiers, and treatment fluids that include viscosifiers may be usedin a variety of subterranean treatments and oilfield operations.

Maintaining sufficient viscosity in treatment fluids may be importantfor a number of reasons. Viscosity is desirable in drilling operationssince treatment fluids with higher viscosity can, among other things,transport solids, such as drill cuttings, more readily. Maintainingsufficient viscosity is important in fracturing treatments forparticulate transport, as well as to create or enhance fracture width.Particulate transport is also important in sand control treatments, suchas gravel packing. Maintaining sufficient viscosity may be important tocontrol and/or reduce leak-off into the formation, improve the abilityto divert another fluid in the formation, and/or reduce pumpingrequirements by reducing friction in the well bore. At the same time,while maintaining sufficient viscosity of a treatment fluid often isdesirable, it also may be desirable to maintain the viscosity of thetreatment fluid in such a way that the viscosity may be reduced at aparticular time, inter alia, for subsequent recovery of the fluid fromthe formation.

To provide the desired viscosity, polymeric viscosifiers are commonlyadded to the treatment fluids. A viscosifier may include any substancethat is capable of increasing the viscosity of a fluid, for example, byforming a gel and/or solid. Examples of commonly used polymericviscosifiers include, but are not limited to guar gums and derivativesthereof, cellulose derivatives, biopolymers, and the like. In hightemperature wells, drilling fluid viscosity can be difficult to controlwith polymeric viscosifiers alone. In some cases, clay material may beadded to increase the viscosity of the drilling fluid at hightemperatures. However, these materials can damage formations and may beundesirable in production zones.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments ofthe present disclosure and should not be used to limit or define theclaims.

FIG. 1 is a schematic diagram of a wellbore drilling assembly used inaccordance with certain embodiments of the present disclosure;

FIGS. 2A and 2B are photographs of an example of a thermally responsivehydrogel before and after injection into water at 37° C., in accordancewith certain embodiments of the present disclosure;

FIG. 3 is a plot of data relating to the viscosity of a 12.0 lbs/galdrilling fluid including a thermally responsive hydrogel with a singlethickening transition temperature, in accordance with certainembodiments of the present disclosure;

FIG. 4 is a plot of data relating to the viscosity of a 12.0 lbs/galdrilling fluid including a thermally responsive hydrogel with twothickening transition temperatures, in accordance with certainembodiments of the present disclosure;

FIG. 5 is a plot of data relating to the viscosity of a 12.0 lbs/galdrilling fluid including a thermally responsive hydrogel with seventhickening transition temperatures, in accordance with certainembodiments of the present disclosure;

FIG. 6 is a plot of data relating to the viscosity of a 16.0 lbs/galdrilling fluid including a thermally responsive hydrogel with a singlethickening transition temperature, in accordance with certainembodiments of the present disclosure;

FIG. 7 is a plot of data relating to the viscosity of a 16.0 lbs/galdrilling fluid including a thermally responsive hydrogel with twothickening transition temperatures, in accordance with certainembodiments of the present disclosure; and

FIG. 8 is a plot of data relating to the viscosity of a 16.0 lbs/galdrilling fluid including a thermally responsive hydrogel with seventhickening transition temperatures, in accordance with certainembodiments of the present disclosure.

While embodiments of this disclosure have been depicted, suchembodiments do not imply a limitation on the disclosure, and no suchlimitation should be inferred. The subject matter disclosed is capableof considerable modification, alteration, and equivalents in form andfunction, as will occur to those skilled in the pertinent art and havingthe benefit of this disclosure. The depicted and described embodimentsof this disclosure are examples only, and not exhaustive of the scope ofthe disclosure.

DESCRIPTION OF CERTAIN EMBODIMENTS

Illustrative embodiments of the present disclosure are described indetail herein. In the interest of clarity, not all features of an actualimplementation may be described in this specification. It will of coursebe appreciated that in the development of any such actual embodiment,numerous implementation-specific decisions may be made to achieve thespecific implementation goals, which may vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthe present disclosure.

The present disclosure relates to methods for treating subterraneanformations, and to methods for using treatment fluids that includethermally responsive viscosifiers in subterranean formations. Morespecifically, the present disclosure provides methods for introducing atreatment fluid that includes an aqueous base fluid and a thermallyresponsive hydrogel into a location (e.g., at least a portion of asubterranean formation). In some embodiments, the thermally responsivehydrogel may include at least one thermoresponsive polymer. In someembodiments, a drilling fluid that includes the aqueous base fluid andthe thermally responsive hydrogel may be used to drill at least aportion of a wellbore in a subterranean formation. In certainembodiments, the thermally responsive hydrogel may include athermoresponsive polymer that may undergo an at least partiallyreversible thickening transition at about, or above, a thickeningtransition temperature.

Among the many advantages to the methods of the present disclosure, onlysome of which are alluded to herein, certain embodiments of the methodsof the present disclosure may, among other benefits, provide for hightemperature viscosity in an aqueous fluid (e.g., an aqueous fluidlocated in a subterranean formation) by undergoing a thickeningtransition at a temperature. In certain embodiments, the thermallyresponsive hydrogels of the present disclosure may provide an enhancedability to thicken aqueous-based fluids at high-temperatures as comparedto certain other viscosifiers, at least in part due to a reversibilityof the thickening transition. In some embodiments, the thermallyresponsive hydrogels of the present disclosure may provide moreeffective thickening of aqueous-based fluids because the thickeningtransition corresponds to a phase change of the thermally responsivehydrogels, and not a chemical reaction as in certain other viscosifiers.In certain embodiments, the thermally responsive hydrogels of thepresent disclosure may provide an enhanced ability to thickenaqueous-based fluids in oilfield operations by providing the ability toat least partially solidify at high temperatures (e.g. at one or more ofthe temperature ranges referenced below). In other embodiments, thethermally responsive hydrogels of the present disclosure may provide anenhanced ability to thicken aqueous-based fluids in oilfield operationsby providing the ability to return to a liquid state when cooled to alower temperature. In certain embodiments, the thermally responsivehydrogels of the present disclosure may provide an enhanced ability tothicken aqueous-based fluids in oilfield operations by providing theability to tune the temperature of the thickening transition by changingthe composition of the thermally responsive hydrogel. In someembodiments, the thermally responsive hydrogels of the presentdisclosure may provide increased high-temperature performance forcuttings transport and/or barite sag as compared to certain otherviscosifiers. In other embodiments, the thermally responsive hydrogelsof the present disclosure may reduce and/or avoid the need to use claymaterial in production zones to increase the high temperature viscosityof a fluid. In certain embodiments, this may reduce and/or avoid damageto the subterranean formation.

Without limiting the disclosure to any particular theory or mechanism,it is believed that the thermally responsive hydrogels of the presentdisclosure may include thermoresponsive polymers that exist, forexample, in contracted, coiled states at lower temperatures where theymay impart little viscosity to a fluid. In certain embodiments, upon anincrease in temperature, the thermoresponsive polymers may un-coil orexpand to a point of very high chain entanglement amongst differentpolymer chains, which may lead to an increase in viscosity of the fluidand/or solidification of the thermally responsive hydrogel. In someembodiments, this transition may initiate at a specific temperature andin some cases may occur relatively rapidly. In other embodiments, atlower temperatures it is believed that intramolecular forces withinindividual thermoresponsive polymers may dominate and lead to acollapsed structure. In certain embodiments, upon an increase intemperature, the thermal vibrational energy may increase to overcome theintramolecular forces within the individual thermoresponsive polymersand allow intermolecular attractive forces between polymer chains tooccur. In turn, this may lead to an increase in viscosity and/or causesolid-state mechanical properties to develop (e.g. stiffness, toughness,and the like).

Treatment fluids often contain additives to impart desired physicaland/or chemical characteristics to the fluid. Viscosifiers control andchange the viscosity of treatment fluids. Without viscosity control, theviscosity of the treatment fluid could undesirably change as a result oftemperature variation during the treatment fluid's transit from the wellsurface to the bottom of the wellbore and back. The thermally responsivehydrogels of the present disclosure may be used in a variety ofapplications and environments in which maintaining sufficient viscosityin treatment fluids may be important. Examples of applications suitablefor certain embodiments of the present disclosure may include, but arenot limited to use in subterranean formations, and/or downholeapplications (e.g., drilling, fracturing, completions, oil production).In certain embodiments, the thermally responsive hydrogels may beapplicable to injection wells, monitoring wells, and/or productionwells, including hydrocarbon or geothermal wells and wellbores. In otherembodiments, the thermally responsive hydrogels may be introduced into asubterranean formation, for example, via a wellbore penetrating at leasta portion of a subterranean formation. Maintaining sufficient viscosityin treatment fluids is important for a number of reasons, including, butnot limited to, particulate transport, wellbore stability, controland/or reduction of fluid loss into the subterranean formation, and/ordiversion of the flow of fluids present within the subterraneanformation to other portions of the formation.

Treatment fluids can be used in a variety of above ground andsubterranean treatment operations. As used herein, the terms “treat,”“treatment,” “treating,” and grammatical equivalents thereof refer toany above ground or subterranean operation that uses a fluid inconjunction with achieving a desired function and/or for a desiredpurpose. Use of these terms does not imply any particular action by thetreatment fluid. Illustrative treatment operations can include, forexample, surface facilities operations, fracturing operations, gravelpacking operations, acidizing operations, scale dissolution and removal,consolidation operations, and the like.

In certain embodiments, a treatment fluid including an aqueous basefluid and a thermally responsive hydrogel may be provided. Depending onthe type of treatment to be performed, the treatment fluid may includeany treatment fluid known in the art. Treatment fluids that may beuseful in accordance with the present disclosure include, but are notlimited to, drilling fluids, cement fluids, lost circulation fluids,stimulation fluids (e.g., a fracturing fluids or an acid stimulationfluids), completion fluids, conformance fluids (e.g., water or gasshutoff fluids), sand control fluids (e.g., formation or proppantconsolidating fluids), workover fluids, and/or any combination thereof.

The thermally responsive hydrogels of the present disclosure may bedispersed in an aqueous phase of the treatment fluid. In someembodiments, a thermally responsive hydrogel may include a material thatis a highly absorbent, three-dimensional network of polymer chains. Insome embodiments, the thermally responsive hydrogel may increase theviscosity of a fluid at or above a thickening transition temperature. Inother embodiments, at lower temperatures (e.g. a temperature below theone or more thickening transition temperature ranges referenced below)the thermally responsive hydrogel may be part of a continuous phase ofthe treatment fluid. In some embodiments, the thermally responsivehydrogel may become a solid at high temperatures (e.g. at or above oneof the thickening transition temperature ranges referenced below). Incertain embodiments, the solid thermally responsive hydrogel mayincrease the viscosity of the treatment fluid. In some embodiments, thethermally responsive hydrogel may thicken a fluid as the temperature ofthe fluid increases by undergoing a thickening transition that is an atleast partially reversible thickening transition. In certainembodiments, the thickening transition may correspond to a phase changeof the thermally responsive hydrogel. In certain embodiments, the phasechange may be a liquid to solid phase change. In certain embodiments,the thermally responsive hydrogel may thicken a fluid as the temperatureof the fluid increases without a chemical reaction occurring.

In certain embodiments, the thermally responsive hydrogel may improvethe particulate transport of a fluid and/or may mitigate weightingmaterial sag at higher temperatures in a wellbore. In other embodiments,the thermally responsive hydrogel may act as a neutral density particlethat may improve sag performance. In certain embodiments, the thermallyresponsive hydrogel may improve fluid loss control. In otherembodiments, the thermally responsive hydrogel may be used in weightedand/or viscous sweeps in high temperature and high pressure (HTHP)wells.

The treatment fluids used in accordance with the methods andcompositions of the present disclosure may include an aqueous basefluid. As used herein, the term “base fluid” refers to the majorcomponent of the fluid (as opposed to components dissolved and/orsuspended therein), and does not indicate any particular condition orproperty of that fluid such as its mass, amount, pH, etc. Aqueous basefluids that may be suitable for use in the methods and systems of thepresent disclosure may include water from any source. Such aqueous basefluids may include fresh water, salt water (e.g., water containing oneor more salts dissolved therein), brine (e.g., saturated salt water),seawater, and/or any combination thereof. The aqueous base fluids may befrom a source that does not contain compounds that adversely affectother components of a fluid. In certain embodiments of the presentdisclosure, the aqueous base fluids may include one or more ionicspecies, such as those formed by salts dissolved in water. For example,seawater and/or produced water may include a variety of divalentcationic species dissolved therein.

In certain embodiments, the density of the aqueous base fluid may beadjusted, among other purposes, to provide additional particulatetransport and suspension in the compositions of the present disclosure.In certain embodiments, the pH of the aqueous base fluid may be adjusted(e.g., by a buffer or other pH adjusting agent) to a specific level,which may depend on, among other factors, the types of thermallyresponsive hydrogels, and/or other additives included in the fluid. Oneof ordinary skill in the art, with the benefit of this disclosure, willrecognize when such density and/or pH adjustments are appropriate. Incertain embodiments, the treatment fluids may include a mixture of oneor more fluids and/or gases, including but not limited to emulsions,foams, and the like.

The thermally responsive hydrogels used in accordance with the methodsof the present disclosure may include at least one thermoresponsivepolymer. In certain embodiments, the thermoresponsive polymer mayinclude at least one monomer that may include, but is not limited to,N-isopropylacrylamide, hydroxyethyl methacrylate, acrylamide,N,N-diethylacrylamide, N-tert-butylacrylamide, butyl acrylate, ethylacrylate, propyl acrylate, methacrylamide, methacrylates, methyl vinylether, N-vinyl-caprolactam, polypeptides, ethylene oxide, propyleneoxide, pluronic F-127, chitosan, any salt thereof, and/or anycombination thereof.

In certain embodiments, the thermoresponsive polymer may be a copolymer.In other embodiments, the copolymer may include at least one firstmonomer and at least one second monomer, and the first monomer and thesecond monomer may be different monomers. In certain embodiments, thefirst monomer may be N-isopropylacrylamide. In certain embodiments, thesecond monomer may be N-tert-butylacrylamide. In certain embodiments,the second monomer may be butylacrylate. In other embodiments, the firstmonomer may be N-isopropylacrylamide and the second monomer may beN-tert-butylacrylamide. In certain embodiments, the first monomer may beN-isopropylacrylamide and the second monomer may be butylacrylate. Inother embodiments, the thermoresponsive polymer may further include oneor more other vinyl monomers. In some embodiments, including one or morevinyl monomers in the thermoresponsive polymer may reduce the cost andincrease the salt tolerance of the thermally responsive hydrogel.

In certain embodiments, the thermoresponsive polymer may further includeone or more other suitable monomers as one of ordinary skill in the artwill recognize with the benefit of this disclosure.

In certain embodiments, the thermally responsive hydrogel may include atleast one thermoresponsive polymer that includes water and apoly(N-alkylacrylamide) copolymer, where alkyl may refer to a C₁₋₆ alkylgroup. In other embodiments, the poly(N-alkylacrylamide) copolymer mayinclude a first monomer that is an N-alkylacrylamide and a secondmonomer that may include, but is not limited to, N-alkylacrylamide,N-isopropylacrylamide, hydroxyethyl methacrylate, acrylamide,N,N-diethylacrylamide, N-tert-butylacrylamide, butyl acrylate, ethylacrylate, propyl acrylate, methacrylamide, a methacrylate, methyl vinylether, N-vinyl-caprolactam, polypeptides, ethylene oxide, propyleneoxide, pluronic F-127, chitosan, any salt thereof, and/or anycombination thereof. Examples of an N-alkylacrylamide monomer include,but are not limited to, N-isopropylacrylamide, acrylamide,N-ethylacrylamide, N-methylacrylamide, N-n-butylacrylamide andN-tert-butylacrylamide.

In certain embodiments, the thermoresponsive polymer may further includean adhesion-enhancing additive. The adhesion-enhancing additive mayinclude, but is not limited to, an Arg-Gly-Asp-Ser amino sequence(RGDS), one or more guanidine-containing compounds, manganese(II)chloride tetrahydrate, and any combination thereof. Examples ofguanidine-containing compounds may include, but are not limited to,aganodine, agmatidine, agmatine, ambazone, amiloride, apraclonidine,aptiganel, argatroban, arginine, argininosuccinic acid, asymmetricdimethylarginine, benexate, benzamil, bethanidine, BIT225, blasticidinS, brostallicin, camostat, cariporide, chlorophenylbiguanide,cimetidine, ciraparantag, creatine, creatine ethyl ester, creatinemethyl ester, creatinine, creatinolfosfate, 2-cyanoguanidine,cycloguanil, debrisoquine, dihydrostreptomycin, ditolylguanidine, E-64,ebrotidine, epinastine, eptifibatide, famotidine, glycocyamine,guanabenz, guanadrel, guanazodine, guanethidine, guanfacine, guanidine,guanidine nitrate, guanidinium chloride, guanidinium thiocyanate,5′-guanidinonaltrindole, 6′-guanidinonaltrindole, guanidinopropionicacid, 3-guanidinopropionic acid, guanochlor, guanoxabenz, guanoxan,gusperimus, impromidine, kopexil, laninamivir, leonurine, lombricine,lugduname, metformin, methylarginine, mitoguazone, octopine, OUP-16,pentosidine, peramivir, phosphocreatine, picloxydine, pimagedine,polyhexamethylene guanidine, n-propyl-1-arginine, rimeporide,robenidine, saxitoxin, siguazodan, streptomycin, sucrononic acid,sulfaguanidine, synthalin, TAN-1057 A, TAN-1057 C, tegaserod, terbogrel,1,1,3,3-tetramethylguanidine, tetrodotoxin, tomopenem,triazabicyclodecene, UR-AK49, vargulin, VUF-8430, zanamivir, and anycombination thereof.

In certain embodiments, the thermoresponsive polymer may include a firstmonomer and a second monomer at a ratio of from about 99:1 to about50:50 by weight percentage ratio of first monomer:second monomer. Insome embodiments, the thermoresponsive polymer may include a firstmonomer and a second monomer at a ratio of from about 99:1 to about80:20 by weight percentage ratio of first monomer:second monomer. Insome embodiments, the thermoresponsive polymer may include a firstmonomer and a second monomer at a ratio of from about 95:5 by weightpercentage ratio of first monomer:second monomer. In some embodiments,the thermoresponsive polymer may include a first monomer that isN-isopropylacrylamide and a second monomer that is butylacrylate, andthe first monomer and the second monomer may be present at a ratio ofabout 95:5 by weight percentage ratio of first monomer:second monomer.

The thermoresponsive polymer may include the monomers in anyconfiguration and the monomers may be repeated with any frequency orpattern, or in a random nature. One of ordinary skill in the art, withthe benefit of this disclosure, will recognize that, in certainembodiments, a thermoresponsive polymer suitable for use in accordancewith the methods of the present disclosure may be provided in an acidform and/or in a salt form. In certain embodiments, the thermallyresponsive hydrogel may include a thermoresponsive polymer that is ablock copolymer. In some embodiments a block copolymer may clusters ofthe same monomer that form blocks of a repeating unit.

In certain embodiments, the thermoresponsive polymer optionally may beat least partially crosslinked. As used herein, the term “crosslink” andgrammatical derivatives thereof refers to a bond linking one monomer orpolymer chain to another polymer chain. The bond may be any bond, forexample, covalent bond, ionic bond, and the like. One of ordinary skillin the art, with the benefit of this disclosure, will recognizecrosslinkers that are suitable for use in accordance with the methods ofthe present disclosure. As used herein, the term “crosslinker” refers toa compound, element, or ion used to crosslink and that includes two ormore olefinic bonds. Examples of crosslinkers that are suitable for usewith the thermoresponsive polymer of the present disclosure include, butare not limited to, pentaerythritol allyl ether andmethylenebisacrylamide.

In certain embodiments, the thermally responsive hydrogel may be amultipolymer interpenetrating polymeric hydrogel. In other embodiments,the multipolymer interpenetrating polymeric hydrogel may include twoindependent crosslinked components. In certain embodiments, thecrosslinked components may be synthetic and/or natural components, whichmay be contained in a network form. In some embodiments, the thermallyresponsive hydrogel may be a semi-interpenetrating polymeric hydrogel.In certain embodiments, the semi-interpenetrating polymeric hydrogel mayinclude a cross-linked polymer component and a non-cross-linked polymercomponent. In certain embodiments, the thermally responsive hydrogel mayinclude a thermoresponsive polymer that may include at least one monomerthat is grafted onto a cheaper polymeric material (e.g. starch). Thismay provide the properties of the thermally responsive hydrogel at areduced cost.

In certain embodiments, the treatment fluids of the present disclosuremay exhibit a viscosity of from about 2 centipoise (cP) to about 200 cP(for example, as measured with a rotational viscometer or a BrookfieldBF35 Viscometer (Ametek®, Inc. Corp., Pennsylvania)). In someembodiments, the treatment fluids of the present disclosure may exhibita viscosity of from about 25 cP to about 200 cP. In some embodiments,the treatment fluids of the present disclosure may exhibit a viscosityof from about 25 cP to about 50 cP. In some embodiments, the treatmentfluids of the present disclosure may exhibit a viscosity of from about50 cP to about 100 cP. In some embodiments, the treatment fluids of thepresent disclosure may exhibit a viscosity of from about 2 cP to about25 cP. In some embodiments, the treatment fluids of the presentdisclosure may exhibit a viscosity of from about 2 cP to about 10 cP. Incertain embodiments, the composition of a treatment fluid including athermally responsive hydrogel may be altered to exhibit and/or maintaina certain viscosity at a certain temperature. In certain embodiments,this may involve altering the composition of a thermoresponsive polymerincluded in the thermally responsive hydrogel to tune its thickeningtransition temperature.

The thermally responsive hydrogels of the present disclosure may includea thermoresponsive polymer that undergoes a thickening transition thatresults in the viscosity of the treatment fluid increasing to aviscosity of from about 2 cP to about 250 cP at about or above athickening transition temperature. In some embodiments, the thermallyresponsive hydrogels of the present disclosure may include athermoresponsive polymer that undergoes a thickening transition thatresults in the viscosity of the treatment fluid increasing to aviscosity as low as any of 2, 3, 4, 6, 8, 10, 20, and 50 cP. In certainembodiments, the thermally responsive hydrogels of the presentdisclosure may include a thermoresponsive polymer that undergoes athickening transition that results in the viscosity of the treatmentfluid increasing to a viscosity as high as any of 20, 40, 60, 80, 100,200, and 250 cP. In certain embodiments, the thermally responsivehydrogels of the present disclosure may include a thermoresponsivepolymer that undergoes a thickening transition that results in theviscosity of the treatment fluid increasing to a viscosity of from about2 cP to about 80 cP, in other embodiments, about 4 cP to about 60 cP, inother embodiments, about 8 cP to about 40 cP, in other embodiments,about 20 cP to about 100 cP, in other embodiments, about 20 cP to about60 cP, in other embodiments, about 100 cP to about 250 cP.

The thermally responsive hydrogel of the present disclosure may includea thermoresponsive polymer that undergoes a thickening transition at athickening transition temperature of from about 30° C. (86° F.) to about210° C. (410° F.). In certain embodiments, the thermally responsivehydrogel of the present disclosure may include a thermoresponsivepolymer that undergoes a thickening transition at a thickeningtransition temperature as low as any of 30, 35, 40, 45, 50, 55, 60, 65,70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, and 130° C. Incertain embodiments, a thermally responsive hydrogel of the presentdisclosure may include a thermoresponsive polymer that undergoes athickening transition at a thickening transition temperature as high asany of 130, 140, 150, 160, 170, 180, 190, 200 and 210° C. In certainembodiments, a treatment fluid including the thermally responsivehydrogel may be introduced into at least a portion of a subterraneanformation wherein the thickening transition temperature at which athermoresponsive polymer included in the thermally responsive hydrogelundergoes a thickening transition is from about 30° C. (86° F.) to about210° C. (410° F.), in other embodiments, about 50° C. (122° F.) to about210° C. (410° F.), in other embodiments, about 75° C. (167° F.) to about210° C. (410° F.), in other embodiments, about 100° C. (212° F.) toabout 210° C. (410° F.), in other embodiments, about 125° C. (257° F.)to about 210° C. (410° F.), in other embodiments, about 125° C. (257°F.) to about 190° C. (374° F.), in other embodiments, about 125° C.(257° F.) to about 170° C. (338° F.), in other embodiments, about 125°C. (257° F.) to about 150° C. (302° F.). In certain embodiments, thethickening transition may include a liquid-to-solid phase change thatoccurs at about or above the thickening transition temperature. Incertain embodiments, the thickening transition may be at least partiallyreversible, e.g. a solid thermally responsive hydrogel may become atleast partially a liquid thermally responsive hydrogel as thetemperature of the thermally responsive hydrogel is decreased to atemperature below the thickening transition temperature.

In some embodiments, the composition of the thermoresponsive polymers ofthe present disclosure may be altered to tune the thickening transitiontemperature. In certain embodiments, the composition of thethermoresponsive polymer may be altered to tune the thickeningtransition temperature at which a liquid-to-solid phase change occurs.In certain embodiments, the composition of the thermoresponsive polymermay be altered, for example, by changing the polymer composition,changing the polymer configuration, use of crosslinkers, addition ofadditives, and the like.

The thermally responsive hydrogel of the present disclosure may includea plurality of thermoresponsive polymers. In certain embodiments, theplurality of thermoresponsive polymers may have a plurality ofthickening transition temperatures. In some embodiments, the thermallyresponsive hydrogel may include two, three, four, five, six, seven,eight, nine, or ten different thermoresponsive polymers. In otherembodiments, the thermally responsive hydrogel may include more than tenthermoresponsive polymers. In certain embodiments, the inclusion of aplurality of thermoresponsive polymers in the thermally responsivehydrogel may provide a more gradual liquid-to-solid phase change and/orincrease in viscosity with increasing temperature of the treatment fluidor the fluid in which the thermally responsive hydrogel is present.

The thermally responsive hydrogel used in accordance with the methods ofthe present disclosure should be present in a fluid in an amountsufficient to provide a desired viscosity at or above a thickeningtransition temperature. In certain embodiments, the thermally responsivehydrogel may be present in the fluid in an amount from about 1% to about20% by weight of the fluid. In certain embodiments, the thermallyresponsive hydrogel may be present in the fluid in an amount from about5% to about 20% by weight of the fluid. In certain embodiments, thethermally responsive hydrogel may be present in the fluid in an amountfrom about 10% to about 15% by weight of the fluid. In certainembodiments, the thermally responsive hydrogel may be present in thefluid in an amount of about 20% by weight of the fluid. In someembodiments, the thermally responsive hydrogel may be present in thefluid in an amount from about 1% to about 4%, in other embodiments, fromabout 4% to about 8%, in other embodiments, from about 8% to about 12%,in other embodiments, from about 12% to about 16%, and in otherembodiments, from about 16% to about 20% by weight of the fluid.

In certain embodiments, the thermally responsive hydrogel may form asolid thermally responsive hydrogel at about, or above, a thickeningtransition temperature (e.g. at or above one or more of the thickeningtransition temperature ranges referenced above). In certain embodiments,the solid thermally responsive hydrogel may be present in a fluid atabout, or above, a thickening transition temperature in an amount fromabout 0.01 to about 0.2 by volume fraction of solids of the fluid. Incertain embodiments, the solid thermally responsive hydrogel may bepresent in the fluid at about, or above, a thickening transitiontemperature in amount from about 0.04 to about 0.2 by volume fraction ofsolids of the fluid. In certain embodiments, the solid thermallyresponsive hydrogel may be present in the fluid at about, or above, athickening transition temperature in amount from about 0.04 to about 0.1by volume fraction of solids of the fluid. In certain embodiments, thesolid thermally responsive hydrogel may be present in the fluid inamount from about 0.01 to about 0.04, in other embodiments, from about0.04 to about 0.08, in other embodiments, from about 0.08 to about 0.12,in other embodiments, from about 0.12 to about 0.16, in otherembodiments, from about 0.16 to about 0.20 by volume fraction of solidsof the fluid. As used herein, “volume fraction of solids” refers to theratio of the volume of solids in a fluid to the total volume.

In certain embodiments, the treatment fluids used in accordance with themethods of the present disclosure optionally may include any number ofadditional additives. Examples of such additional additives include, butare not limited to, salts, surfactants, acids, proppant particulates,diverting agents, additional fluid loss control additives, gas,nitrogen, carbon dioxide, surface modifying agents, tackifying agents,foamers, corrosion inhibitors, scale inhibitors, catalysts, clay controlagents, shale inhibitors, biocides, friction reducers, antifoam agents,bridging agents, flocculants, H₂S scavengers, CO₂ scavengers, oxygenscavengers, lost circulation materials, lubricants, additionalviscosifiers, breakers, weighting agents, relative permeabilitymodifiers, resins, wetting agents, coating enhancement agents, filtercake removal agents, antifreeze agents (e.g., ethylene glycol orpolyethylene glycol), and the like. In certain embodiments, one or moreof these optional additives (e.g., a shale inhibitor) may be added tothe treatment fluid and/or activated after the thermally responsivehydrogel has been at least partially hydrated in the fluid. A personskilled in the art, with the benefit of this disclosure, will recognizethe types of additives that may be included in the fluids of the presentdisclosure for a particular application.

In certain embodiments, the treatment fluids used in accordance with themethods of the present disclosure optionally may include a weightingagent. In some embodiments, the weighting agent may be added to producea desired density in the treatment fluid. In certain embodiments, theweighting agent may include barite. Examples of other weighting agentsinclude, but are not limited to, hematite, magnetite, iron oxides,illmenite, siderite, celestite, dolomite, olivine, calcite, magnesiumoxides, halites, calcium carbonate, strontium sulfate, manganesetetraoxide, and the like. A person skilled in the art, with the benefitof this disclosure, will recognize the types of weighting agent that maybe included in the fluids of the present disclosure for a particularapplication.

In certain embodiments, the treatment fluids including a thermallyresponsive hydrogel optionally may include one or more surfactants. Thesurfactant may, among other purposes, help disperse the thermallyresponsive hydrogel and/or other additives in a treatment fluid.Examples of surfactants that may be suitable for use may include, butare not limited to, an alkoxylated alkyl alcohol and salts thereof, analkoxylated alkyl phenol and salts thereof, an alkyl or aryl sulfonate,a sulfate, a phosphate, a carboxylate, a polyoxyalkyl glycol, a fattyalcohol, a polyoxyethylene glycol sorbitan alkyl ester, a sorbitan alkylester, a polysorbate, a glucoside, a quaternary amine compound, an amineoxide surfactant, or any combination thereof.

The treatment fluids of the present disclosure may be prepared using anysuitable method and/or equipment (e.g., blenders, mixers, stirrers,etc.) known in the art at any time prior to their use. The treatmentfluids may be prepared at a well site or at an offsite location.

The present disclosure in some embodiments provides methods for usingthe treatment fluids to carry out a variety of subterranean treatmentsor operations, including but not limited to, drilling operations,cementing operations, fracturing operations, gravel packing operations,workover operations, and the like. In some embodiments, the treatmentfluids of the present disclosure may be drilling fluids used fordrilling a wellbore into a subterranean formation. In certainembodiments, the drilling fluids may include a low concentration ofsolids, for example, the drilling fluids may be substantially free ofadded clays or other types of solids which may plug formation zones. Asused herein, the term “added clay” refers to a clay added to a drillingfluid prior to the introduction of the drilling fluid into asubterranean formation.

In certain embodiments, a treatment fluid including a thermallyresponsive hydrogel may be introduced into a subterranean formation. Incertain embodiments, the subterranean formation may have a bottom holetemperature of from about 66° C. (150° F.) to about 204° C. (400° F.).In certain embodiments, the subterranean formation may have a bottomhole temperature of from about 93° C. (200° F.) to about 204° C. (400°F.). In certain embodiments, the subterranean formation may have abottom hole temperature of from about 93° C. (200° F.) to about 177° C.(350° F.). In certain embodiments, the subterranean formation may have abottom hole temperature of at least 177° C. (350° F.). In someembodiments, the treatment fluid including the thermally responsivehydrogel may be used to drill at least a portion of a wellbore in thesubterranean formation. In some embodiments, the treatment fluid maycirculate through the wellbore while drilling into the subterraneanformation. In some embodiments, the treatment fluid including thethermally responsive hydrogel may be introduced into a wellbore thatpenetrates a subterranean formation. In certain embodiments, thetreatment fluid including a thermally responsive hydrogel may be chilledbefore being introduced into a location (e.g. a subterranean formation).In certain embodiments, this may allow for the management of thetreatment fluid such that it may be pumped to a specific location beforethe thermally responsive hydrogel at least partially solidifies. Incertain embodiments, the solidification of the thermally responsivehydrogel may be at least partially reversible, e.g. a solid thermallyresponsive hydrogel may become at least partially a liquid thermallyresponsive hydrogel as the temperature of the thermally responsivehydrogel is decreased to a temperature below a thickening transitiontemperature. In certain embodiments, a bottom hole temperature may behigh (e.g. one or more of the temperatures referenced above) and thetreatment fluid may be chilled to a temperature much lower than ambient(e.g. to a temperature below 10° C.). In other embodiments, a freezingpoint inhibitor (e.g. ethylene glycol or polyethylene glycol and/or asalt) may be included and the treatment fluid may be chilled to atemperature at about or below 0° C.

In some embodiments, the methods of the present disclosure may includefoaming the treatment fluid by incorporating air, nitrogen, anappropriate foamer, glass spheres, or any combination thereof into thefluid. In certain embodiments, the treatment fluid may be introducedinto the wellbore using one or more pumps. In some embodiments, thethermally responsive hydrogel, treatment fluids, and/or additionaladditives may be used in treating a portion of a subterranean formation,for example, in acidizing treatments such as matrix acidizing orfracture acidizing. In some embodiments, the treatment fluid includingthe thermally responsive hydrogel may be introduced at a pressuresufficient to create or enhance one or more fractures within thesubterranean formation (e.g., hydraulic fracturing).

In certain embodiments of the present disclosure, the treatment fluidsof the present disclosure may be introduced into a subterraneanformation, a wellbore penetrating a subterranean formation, tubing(e.g., pipeline), and/or a container using any method or equipment knownin the art. Introduction of the treatment fluids of the presentdisclosure may in such embodiments include delivery via any of a tube,umbilical, pump, gravity, and combinations thereof. The treatment fluidsof the present disclosure may, in various embodiments, be delivereddownhole (e.g., into the wellbore) or into top-side flowlines/pipelinesor surface treating equipment. For example, in certain embodiments, thetreatment fluids of the present disclosure may be introduced into asubterranean formation and/or wellbore using batch treatments, squeezetreatments, continuous treatments, and/or combinations thereof.

For example, in certain embodiments, the thermally responsive hydrogel,treatment fluids, and/or additional additives of the present disclosuremay be introduced into a subterranean formation and/or wellbore usingbatch treatments, squeeze treatments, continuous treatments, and/orcombinations thereof. In certain embodiments, a batch treatment may beperformed in a subterranean formation by stopping production from thewell and pumping a certain amount of the thermally responsive hydrogel,treatment fluids, and/or additional additives into a wellbore, which maybe performed at one or more points in time during the life of a well. Inother embodiments, a squeeze treatment may be performed by dissolvingthe thermally responsive hydrogel, treatment fluids, and/or additionaladditives in a suitable solvent at a suitable concentration andsqueezing that solvent carrying the thermally responsive hydrogel oradditional additives downhole into the formation, allowing productionout of the formation to bring the thermally responsive hydrogel oradditional additives to the desired location.

In some embodiments, the present disclosure provides methods for usingthe thermally responsive hydrogel, treatment fluids, and/or additionaladditives to carry out a variety of subterranean treatments, includingbut not limited to, preflush treatments, afterflush treatments,hydraulic fracturing treatments, acidizing treatments, sand controltreatments (e.g., gravel packing), “frac-pack” treatments, wellboreclean-out treatments, drilling operations, and other operations where atreatment fluid may be useful. Such treatment fluids may include, butare not limited to, drilling fluids, preflush fluids, afterflush fluids,fracturing fluids, acidizing fluids, gravel packing fluids, packerfluids, spacer fluids, and the like.

In the methods of the present disclosure, the thermally responsivehydrogel may be added to, or included in, a treatment fluid in anyamount that may effectively thicken a fluid to be treated by a desiredamount at a desired temperature. In certain embodiments, an initialamount of thermally responsive hydrogel may be added to a treatmentfluid followed by subsequent, additional amounts. This technique may beused to increase and/or maintain a concentration of thermally responsivehydrogel that may be sufficient to maintain a desired viscosity in afluid to be treated throughout the course of a given operation.

The treatment fluids of the present disclosure may directly orindirectly affect one or more components or pieces of equipmentassociated with the preparation, delivery, recapture, recycling, reuse,and/or disposal of the disclosed treatment fluids. For example, and withreference to FIG. 1, the disclosed treatment fluids may directly orindirectly affect one or more components or pieces of equipmentassociated with an exemplary wellbore drilling assembly 100, accordingto one or more embodiments. It should be noted that while FIG. 1generally depicts a land-based drilling assembly, those skilled in theart will readily recognize that the principles described herein areequally applicable to subsea drilling operations that employ floating orsea-based platforms and rigs, without departing from the scope of thedisclosure.

As illustrated, the drilling assembly 100 may include a drillingplatform 102 that supports a derrick 104 having a traveling block 106for raising and lowering a drill string 108. The drill string 108 mayinclude, but is not limited to, drill pipe and coiled tubing, asgenerally known to those skilled in the art. A kelly 110 supports thedrill string 108 as it is lowered through a rotary table 112. A drillbit 114 is attached to the distal end of the drill string 108 and isdriven either by a downhole motor and/or via rotation of the drillstring 108 from the well surface. As the bit 114 rotates, it creates aborehole 116 that penetrates various subterranean formations 118.

A pump 120 (e.g., a mud pump) circulates drilling fluid 122 through afeed pipe 124 and to the kelly 110, which conveys the drilling fluid 122downhole through the interior of the drill string 108 and through one ormore orifices in the drill bit 114. The drilling fluid 122 is thencirculated back to the surface via an annulus 126 defined between thedrill string 108 and the walls of the borehole 116. At the surface, therecirculated or spent drilling fluid 122 exits the annulus 126 and maybe conveyed to one or more fluid processing unit(s) 128 via aninterconnecting flow line 130. After passing through the fluidprocessing unit(s) 128, a “cleaned” drilling fluid 122 is deposited intoa nearby retention pit 132 (i.e., a mud pit). While illustrated as beingarranged at the outlet of the wellbore 116 via the annulus 126, thoseskilled in the art will readily appreciate that the fluid processingunit(s) 128 may be arranged at any other location in the drillingassembly 100 to facilitate its proper function, without departing fromthe scope of the scope of the disclosure.

One or more of the disclosed treatment fluids may be added to thedrilling fluid 122 via a mixing hopper 134 communicably coupled to orotherwise in fluid communication with the retention pit 132. The mixinghopper 134 may include, but is not limited to, mixers and related mixingequipment known to those skilled in the art. In other embodiments,however, the disclosed treatment fluids may be added to the drillingfluid 122 at any other location in the drilling assembly 100. In atleast one embodiment, for example, there could be more than oneretention pit 132, such as multiple retention pits 132 in series.Moreover, the retention pit 132 may be representative of one or morefluid storage facilities and/or units where the disclosed treatmentfluids may be stored, reconditioned, and/or regulated until added to thedrilling fluid 122.

As mentioned above, the disclosed treatment fluids may directly orindirectly affect the components and equipment of the drilling assembly100. For example, the disclosed treatment fluids may directly orindirectly affect the fluid processing unit(s) 128 which may include,but is not limited to, one or more of a shaker (e.g., shale shaker), acentrifuge, a hydrocyclone, a separator (including magnetic andelectrical separators), a desilter, a desander, a separator, a filter(e.g., diatomaceous earth filters), a heat exchanger, any fluidreclamation equipment. The fluid processing unit(s) 128 may furtherinclude one or more sensors, gauges, pumps, compressors, and the likeused store, monitor, regulate, and/or recondition the exemplarytreatment fluids.

The disclosed treatment fluids may directly or indirectly affect thepump 120, which representatively includes any conduits, pipelines,trucks, tubulars, and/or pipes used to fluidically convey the treatmentfluids downhole, any pumps, compressors, or motors (e.g., topside ordownhole) used to drive the treatment fluids into motion, any valves orrelated joints used to regulate the pressure or flow rate of thetreatment fluids, and any sensors (i.e., pressure, temperature, flowrate, etc.), gauges, and/or combinations thereof, and the like. Thedisclosed treatment fluids may also directly or indirectly affect themixing hopper 134 and the retention pit 132 and their assortedvariations.

The disclosed treatment fluids may also directly or indirectly affectthe various downhole equipment and tools that may come into contact withthe treatment fluids such as, but not limited to, the drill string 108,any floats, drill collars, mud motors, downhole motors and/or pumpsassociated with the drill string 108, and any MWD/LWD tools and relatedtelemetry equipment, sensors or distributed sensors associated with thedrill string 108. The disclosed treatment fluids may also directly orindirectly affect any downhole heat exchangers, valves and correspondingactuation devices, tool seals, packers and other wellbore isolationdevices or components, and the like associated with the wellbore 116.The disclosed treatment fluids may also directly or indirectly affectthe drill bit 114, which may include, but is not limited to, roller conebits, PDC bits, natural diamond bits, any hole openers, reamers, coringbits, etc.

While not specifically illustrated herein, the disclosed treatmentfluids may also directly or indirectly affect any transport or deliveryequipment used to convey the treatment fluids to the drilling assembly100 such as, for example, any conduits, pipelines, trucks, tubulars,and/or pipes used to fluidically move the treatment fluids from onelocation to another, any pumps, compressors, or motors used to drive thetreatment fluids into motion, any valves or related joints used toregulate the pressure or flow rate of the treatment fluids, and anysensors (i.e., pressure and temperature), gauges, and/or combinationsthereof, and the like.

An embodiment of the present disclosure is a method includingintroducing a treatment fluid including an aqueous base fluid and athermally responsive hydrogel including at least one thermoresponsivepolymer into at least a portion of a subterranean formation.

Another embodiment of the present disclosure is a method of drilling awellbore in a subterranean formation including using a drilling fluidincluding an aqueous base fluid and a thermally responsive hydrogelincluding at least one thermoresponsive polymer to drill at least aportion of a wellbore in the subterranean formation.

Another embodiment of the present disclosure is a method includingintroducing a treatment fluid including an aqueous base fluid and athermally responsive hydrogel including at least one thermoresponsivepolymer into at least a portion of a subterranean formation; andallowing the at least one thermoresponsive polymer to undergo an atleast partially reversible thickening transition at about, or above, athickening transition temperature.

Another embodiment of the present disclosure is a method includingintroducing a treatment fluid including an aqueous base fluid and athermally responsive hydrogel including at least one thermoresponsivepolymer into at least a portion of a subterranean formation, wherein theaqueous base fluid includes at least one component selected from thegroup consisting of: water, salt water, brine, seawater, and anycombination thereof. Optionally in this embodiment or any otherembodiment disclosed herein, the thermally responsive hydrogel ispresent in the treatment fluid in an amount from about 1% to about 20%by weight of the treatment fluid. Optionally in this embodiment or anyother embodiment of the present disclosure, the method further includeschilling the treatment fluid prior to introducing the treatment fluidinto the at least a portion of the subterranean formation. Optionally inthis embodiment or any other embodiment of the present disclosure, themethod further includes circulating the treatment fluid through awellbore while drilling into the subterranean formation. Optionally inthis embodiment or any other embodiment of the present disclosure, thethermally responsive hydrogel includes a hydrogel selected from thegroup consisting of: a multipolymer interpenetrating polymeric hydrogel,a semi-interpenetrating polymer hydrogel, and any combination thereof.Optionally in this embodiment or any other embodiment of the presentdisclosure, the at least one thermoresponsive polymer includes at leastone monomer selected from the group consisting of:N-isopropylacrylamide, hydroxyethyl methacrylate, acrylamide,N,N-diethylacrylamide, N-ethylacrylamide, N-methylacrylamide,N-n-butylacrylamide, N-tert-butylacrylamide, butyl acrylate, ethylacrylate, propyl acrylate, methacrylamide, a methacrylate, methyl vinylether, N-vinyl-caprolactam, polypeptides, ethylene oxide, propyleneoxide, pluronic F-127, chitosan, any salt thereof, and any combinationthereof. Optionally in this embodiment or any other embodiment of thepresent disclosure, the at least one thermoresponsive polymer undergoesa thickening transition at a thickening transition temperature of fromabout 30° C. to about 210° C. Optionally in this embodiment or any otherembodiment of the present disclosure, a viscosity of the treatment fluidincreases to a viscosity of from about 2 cP to about 250 cP at about orabove a thickening transition temperature. Optionally in this embodimentor any other embodiment of the present disclosure, the thermallyresponsive hydrogel includes a plurality of thermoresponsive polymershaving a plurality of thickening transition temperatures.

Another embodiment of the present disclosure is a method of drilling awellbore in a subterranean formation including using a drilling fluidincluding an aqueous base fluid and a thermally responsive hydrogelincluding at least one thermoresponsive polymer to drill at least aportion of a wellbore in the subterranean formation, wherein the aqueousbase fluid includes at least one component selected from the groupconsisting of: water, salt water, brine, seawater, and any combinationthereof. Optionally in this embodiment or any other embodiment disclosedherein, the thermally responsive hydrogel is present in the drillingfluid in an amount from about 1% to about 20% by weight of the drillingfluid. Optionally in this embodiment or any other embodiment of thepresent disclosure, the at least one thermoresponsive polymer includesat least one monomer selected from the group consisting of:N-isopropylacrylamide, hydroxyethyl methacrylate, acrylamide,N,N-diethylacrylamide, N-ethylacrylamide, N-methylacrylamide,N-n-butylacrylamide, N-tert-butylacrylamide, butyl acrylate, ethylacrylate, propyl acrylate, methacrylamide, a methacrylate, methyl vinylether, N-vinyl-caprolactam, polypeptides, ethylene oxide, propyleneoxide, pluronic F-127, chitosan, any salt thereof, and any combinationthereof. Optionally in this embodiment or any other embodiment of thepresent disclosure, the at least one thermoresponsive polymer undergoesa thickening transition at a thickening transition temperature of fromabout 30° C. to about 210° C. Optionally in this embodiment or any otherembodiment of the present disclosure, a viscosity of the drilling fluidincreases to a viscosity of from about 2 cP to about 250 cP at about orabove a thickening transition temperature. Optionally in this embodimentor any other embodiment of the present disclosure, the thermallyresponsive hydrogel includes a plurality of thermoresponsive polymershaving a plurality of thickening transition temperatures.

Another embodiment of the present disclosure is a method includingintroducing a treatment fluid including an aqueous base fluid and athermally responsive hydrogel including at least one thermoresponsivepolymer into at least a portion of a subterranean formation; andallowing the at least one thermoresponsive polymer to undergo an atleast partially reversible thickening transition at about, or above, athickening transition temperature, wherein the thickening transitiontemperature is from about 30° C. to about 210° C. Optionally in thisembodiment or any other embodiment disclosed herein, a viscosity of thetreatment fluid increases to a viscosity of from about 2 cP to about 250cP at about or above the thickening transition temperature.

To facilitate a better understanding of the present disclosure, thefollowing examples of certain aspects of certain embodiments are given.The following examples are not the only examples that could be givenaccording to the present disclosure and are not intended to limit thescope of the disclosure or claims.

EXAMPLES

The following examples demonstrate calculations conducted to evaluatethe ability of the thermally responsive hydrogel to provide for hightemperature viscosity in a water-based mud according to some embodimentsof the present disclosure. FIGS. 2A and 2B are photographs of an exampleof a thermally responsive hydrogel before (FIG. 2A) and after (FIG. 2B)injection into water at 37° C., demonstrating that the thermallyresponsive hydrogel may form a solid when the temperature of thehydrogel increases to a temperature above the thickening transitiontemperature.

A Krieger-Dougherty modified model was used to predict the impact of theliquid-to-solid phase change of a thermally responsive hydrogel on theapparent viscosity of a fluid in which the thermally responsive hydrogelis present. This modified model demonstrates an increase in theviscosity of the fluid when particles are added, which depends on theconcentration of the particles according to the following equation:

$\begin{matrix}{\frac{\eta}{\eta_{0}} = \left( {1 - \frac{\phi}{\phi_{m}}} \right)^{{- {\lbrack\eta\rbrack}}\phi_{m}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$where η=apparent viscosity of the water-based mud suspension

η₀=apparent viscosity of the continuous fluid medium in the water-basedmud suspension

[η]=the intrinsic viscosity, which is assumed to be 2.5 for spheres inthis calculation

Φ=the volume fraction of solids of the solid thermally responsivehydrogel

and Φ_(m)=the maximum packing fraction of the solid thermally responsivehydrogel.

Equation 1 was combined with the Arrhenius Model (using a simplifiedexponential model) to demonstrate the general performance potential of athermally responsive hydrogel on drilling fluid viscosity according toEquation 2:η(T)=η₀ e ^(−bT)  (Equation 2)where T=the absolute temperature (in Kelvin)and b=a decay composition constant.

Example 1

In this example, the apparent viscosity of a thermally responsivehydrogel including one thermoresponsive polymer with a single thickeningtransition temperature of 243° F. in a 12.0 lbs/gal water-based drillingfluid was calculated using the model described above. A solid weightingagent of barite was added to produce the desired weight of the drillingfluid. The results of these calculations are shown in FIG. 3. Referringnow to FIG. 3, plot 300 shows the apparent viscosity in cP on axis 310against temperature in ° F. on axis 320 for a total volume fraction ofsolids (Vf) of the solid thermally responsive hydrogel, ϕ, of 0 (basefluid 330) 0.08 (340), 0.12 (350), and 0.16 (360). Plot 300 also showsthe change in volume fraction of solids of the solid thermallyresponsive hydrogel on axis 370 against temperature in ° F. on axis 320for ϕ f 0.08 (341), 0.12 (351), and 0.16 (361) as the thickeningtransition at 243° F. takes place. FIG. 3 demonstrates that the apparentviscosity of a fluid that includes a thermally responsive hydrogel isexpected to increase as the thickening transition temperature isreached. The larger the value of ϕ, the larger the apparent viscosityincrease at the transition temperature. FIG. 3 also shows that thevolume fraction of solids of a thermally responsive hydrogel materialwith a single thickening transition temperature is expected to increasein a single step at the thickening transition temperature. These resultsdemonstrate that the thermally responsive hydrogel may increase theapparent viscosity of a drilling fluid upon an increase in temperatureto or above the thickening transition temperature.

Example 2

In this example, the apparent viscosity of a thermally responsivehydrogel including two different thermoresponsive polymers withdifferent thickening transition temperatures of 243 and 318° F. in a12.0 lbs/gal water-based drilling fluid was calculated using the modeldescribed above. A solid weighting agent of barite was added to producethe desired weight of the drilling fluid. The results of thesecalculations are shown in FIG. 4. Referring now to FIG. 4, plot 400shows the apparent viscosity in cP on axis 410 against temperature in °F. on axis 420 for a total volume fraction of solids (Vf) of the solidthermally responsive hydrogel, ϕ, of 0 (base fluid 430) 0.08 (440), 0.12(450), and 0.16 (460). Plot 400 also shows the change in volume fractionof solids of the solid thermally responsive hydrogel on axis 470 againsttemperature in ° F. on axis 320 for ϕ of 0.08 (441), 0.12 (451), and0.16 (461) as the thickening transitions at 243 and 318° F. take place.FIG. 4 demonstrates that the volume fraction of solids of a thermallyresponsive hydrogel material with two thickening transition temperaturesis expected to increase sequentially in a stepwise manner with anincrease at each of the two thickening transition temperatures of 243and 318° F.

Example 3

In this example, the apparent viscosity of a thermally responsivehydrogel that including seven different thermoresponsive polymers withseven different thickening transition temperatures of 243, 268, 293,318, 343, 368 and 318° F. in a 12.0 lbs/gal water-based drilling fluidwas calculated using the model described above. A solid weighting agentof barite was added to produce the desired weight of the drilling fluid.The results of these calculations are shown in FIG. 5. Referring now toFIG. 5, plot 500 shows the apparent viscosity in cP on axis 510 againsttemperature in ° F. on axis 520 for a total volume fraction of solids(Vf) of the solid thermally responsive hydrogel, ϕ, of 0 (base fluid530) 0.08 (540), 0.12 (550), and 0.16 (560). Plot 500 also shows thechange in volume fraction of solids of the solid thermally responsivehydrogel on axis 570 against temperature in ° F. on axis 320 for ϕ of0.08 (541), 0.12 (551), and 0.16 (561) as the thickening transitions at243, 268, 293, 318, 343, 368 and 318° F. take place. FIG. 5 demonstratesthat the volume fraction of solids of a thermally responsive hydrogelmaterial with seven thickening transition temperatures is expected toincrease sequentially with a smooth transition. Thus, differentthermoresponsive polymers with different thickening transitiontemperatures included in a thermally responsive hydrogel may produce amore gradual change in the volume fraction of solids with increasingtemperature.

Example 4

In this example, the apparent viscosity of a thermally responsivehydrogel including one thermoresponsive polymer with a single thickeningtransition temperature of 243° F. in a 16.0 lbs/gal water-based drillingfluid was calculated using the model described above. A solid weightingagent of barite was added to produce the desired weight of the drillingfluid. The results of these calculations are shown in FIG. 6. Referringnow to FIG. 6, plot 600 shows the apparent viscosity in cP on axis 610against temperature in ° F. on axis 620 for a total volume fraction ofsolids (Vf) of the solid thermally responsive hydrogel, ϕ, of 0 (basefluid 630) 0.08 (640), 0.12 (650), and 0.16 (660). Plot 600 also showsthe change in volume fraction of solids of the solid thermallyresponsive hydrogel on axis 670 against temperature in ° F. on axis 620for ϕ of 0.08 (641), 0.12 (651), and 0.16 (661) as the thickeningtransition at 243° F. takes place. FIG. 6 demonstrates that the apparentviscosity of a fluid that includes a thermally responsive hydrogel isexpected to increase as the thickening transition temperature isreached, and that this increase is expected to be larger for a 16.0lbs/gal drilling fluid as compared to the 12.0 lbs/gal drilling fluid inExample 1. The larger the value of ϕ, the larger the expected increasein apparent viscosity at the transition temperature. FIG. 6 also showsthat the volume fraction of solids of a thermally responsive hydrogelmaterial with a single thickening transition temperature is expected toincrease in a single step at the thickening transition temperature.These results demonstrate that the thermally responsive hydrogel mayincrease the apparent viscosity of a drilling fluid upon an increase intemperature to or above the thickening transition temperature, and thatthis increase is related to the weight of the drilling fluid.

Example 5

In this example, the apparent viscosity of a thermally responsivehydrogel including two different thermoresponsive polymers withdifferent thickening transition temperatures of 243 and 318° F. in a16.0 lbs/gal water-based drilling fluid was calculated using the modeldescribed above. A solid weighting agent of barite was added to producethe desired weight of the drilling fluid. The results of thesecalculations are shown in FIG. 7. Referring now to FIG. 7, plot 700shows the apparent viscosity in cP on axis 710 against temperature in °F. on axis 720 for a total volume fraction of solids (Vf) of the solidthermally responsive hydrogel, ϕ, of 0 (base fluid 730) 0.08 (740), 0.12(750), and 0.16 (760). Plot 700 also shows the change in volume fractionof solids of the solid thermally responsive hydrogel on axis 770 againsttemperature in ° F. on axis 720 for ϕ of 0.08 (741), 0.12 (751), and0.16 (761) as the thickening transitions at 243 and 318° F. take place.FIG. 7 demonstrates that the apparent viscosity of a fluid that includesa thermally responsive hydrogel is expected to increase as thethickening transition temperatures are reached, and that these increasesare expected to be larger for a 16.0 lbs/gal drilling fluid as comparedto the 12.0 lbs/gal drilling fluid in Example 2. FIG. 7 alsodemonstrates that the volume fraction of solids of a thermallyresponsive hydrogel material with two thickening transition temperaturesis expected to increase sequentially in a stepwise manner with anincrease at each of the two thickening transition temperatures of 243and 318° F.

Example 6

In this example, the apparent viscosity of a thermally responsivehydrogel including seven different thermoresponsive polymers with sevendifferent thickening transition temperatures of 243, 268, 293, 318, 343,368 and 318° F. in a 16.0 lbs/gal water-based drilling fluid wascalculated using the model described above. A solid weighting agent ofbarite was added to produce the desired weight of the drilling fluid.The results of these calculations are shown in FIG. 8. Referring now toFIG. 8, plot 800 shows the apparent viscosity in cP on axis 810 againsttemperature in ° F. on axis 820 for a total volume fraction of solids(Vf) of the solid thermally responsive hydrogel, ϕ, of 0 (base fluid830) 0.08 (840), 0.12 (850), and 0.16 (860). Plot 800 also shows thechange in volume fraction of solids of the solid thermally responsivehydrogel on axis 870 against temperature in ° F. on axis 820 for ϕ of0.08 (841), 0.12 (851), and 0.16 (861) as the thickening transitions at243, 268, 293, 318, 343, 368 and 318° F. take place. FIG. 8 demonstratesthat the apparent viscosity of a fluid that includes a thermallyresponsive hydrogel is expected to increase as the thickening transitiontemperatures are reached, and that these increases are expected to belarger for a 16.0 lbs/gal drilling fluid as compared to the 12.0 lbs/galdrilling fluid in Example 3. FIG. 8 also demonstrates that the volumefraction of solids of a thermally responsive hydrogel material withseven thickening transition temperatures is expected to increasesequentially with a smooth transition. Thus, different thermoresponsivepolymers with different thickening transition temperatures included inthe thermally responsive hydrogel may produce a more gradual change inthe volume fraction of solids with increasing temperature.

Therefore, the present disclosure is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent disclosure may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. While numerous changes may be made bythose skilled in the art, such changes are encompassed within the spiritof the subject matter defined by the appended claims. Furthermore, nolimitations are intended to the details of construction or design hereinshown, other than as described in the claims below. It is thereforeevident that the particular illustrative embodiments disclosed above maybe altered or modified and all such variations are considered within thescope and spirit of the present disclosure. In particular, every rangeof values (e.g., “from about a to about b,” or, equivalently, “fromapproximately a to b,” or, equivalently, “from approximately a-b”)disclosed herein is to be understood as referring to the power set (theset of all subsets) of the respective range of values. The terms in theclaims have their plain, ordinary meaning unless otherwise explicitlyand clearly defined by the patentee.

What is claimed is:
 1. A method comprising: introducing a treatmentfluid comprising an aqueous base fluid and a thermally responsivehydrogel comprising at least one thermoresponsive polymer into at leasta portion of a subterranean formation; allowing the thermally responsivehydrogel to reach a thickening transition temperature, wherein thethermally responsive hydrogel undergoes a liquid-to-solid phase changeat or above the thickening transition temperature; and allowing thetreatment fluid to at least partially solidify in the subterraneanformation, wherein the solid thermally responsive hydrogel is present inthe treatment fluid in an amount from about 0.01 to about 0.2 by volumefraction of solids of the treatment fluid.
 2. The method of claim 1,wherein the aqueous base fluid comprises at least one component selectedfrom the group consisting of: water, salt water, brine, seawater, andany combination thereof.
 3. The method of claim 1 wherein the thermallyresponsive hydrogel is present in the treatment fluid in an amount fromabout 1% to about 20% by weight of the treatment fluid.
 4. The method ofclaim 1, further comprising chilling the treatment fluid prior tointroducing the treatment fluid into the at least a portion of thesubterranean formation.
 5. The method of claim 1 further comprisingcirculating the treatment fluid through a wellbore while drilling intothe subterranean formation.
 6. The method of claim 1, wherein thethermally responsive hydrogel comprises a hydrogel selected from thegroup consisting of: a multipolymer interpenetrating polymeric hydrogel,a semi-interpenetrating polymer hydrogel, and any combination thereof.7. The method of claim 1, wherein the at least one thermoresponsivepolymer comprises at least one monomer selected from the groupconsisting of: N-isopropylacrylamide, hydroxyethyl methacrylate,acrylamide, N,N-diethylacrylamide, N-ethylacrylamide,N-methylacrylamide, N-n-butylacrylamide, N-tert-butylacrylamide, butylacrylate, ethyl acrylate, propyl acrylate, methacrylamide, amethacrylate, methyl vinyl ether, N-vinyl-caprolactam, polypeptides,ethylene oxide, propylene oxide, pluronic F-127, chitosan, any saltthereof, and any combination thereof.
 8. The method of claim 1, whereinthe at least one thermoresponsive polymer undergoes a thickeningtransition at a thickening transition temperature of from about 30° C.to about 210° C.
 9. The method of claim 1, wherein a viscosity of thetreatment fluid increases to a viscosity of from about 2 cP to about 250cP at about or above a thickening transition temperature.
 10. The methodof claim 1, wherein the thermally responsive hydrogel comprises aplurality of thermoresponsive polymers having a plurality of thickeningtransition temperatures.
 11. A method of drilling a wellbore in asubterranean formation, the method comprising: using a drilling fluidcomprising an aqueous base fluid and a thermally responsive hydrogelcomprising at least one thermoresponsive polymer to drill at least aportion of a wellbore in the subterranean formation; allowing thethermally responsive hydrogel to reach a thickening transitiontemperature, wherein the thermally responsive hydrogel undergoes aliquid-to-solid phase change at or above the thickening transitiontemperature; and allowing the drilling fluid to at least partiallysolidify in the subterranean formation, wherein the solid thermallyresponsive hydrogel is present in the drilling fluid in an amount fromabout 0.01 to about 0.2 by volume fraction of solids of the drillingfluid.
 12. The method of claim 11, wherein the aqueous base fluidcomprises at least one component selected from the group consisting of:water, salt water, brine, seawater, and any combination thereof.
 13. Themethod of claim 11 wherein the thermally responsive hydrogel is presentin the drilling fluid in an amount from about 1% to about 20% by weightof the drilling fluid.
 14. The method of claim 11, wherein the at leastone thermoresponsive polymer comprises at least one monomer selectedfrom the group consisting of: N-isopropylacrylamide, hydroxyethylmethacrylate, acrylamide, N,N-diethylacrylamide, N-ethylacrylamide,N-methylacrylamide, N-n-butylacrylamide, N-tert-butylacrylamide, butylacrylate, ethyl acrylate, propyl acrylate, methacrylamide, amethacrylate, methyl vinyl ether, N-vinyl-caprolactam, polypeptides,ethylene oxide, propylene oxide, pluronic F-127, chitosan, any saltthereof, and any combination thereof.
 15. The method of claim 11,wherein the at least one thermoresponsive polymer undergoes a thickeningtransition at a thickening transition temperature of from about 30° C.to about 210° C.
 16. The method of claim 11, wherein a viscosity of thedrilling fluid increases to a viscosity of from about 2 cP to about 250cP at about or above a thickening transition temperature.
 17. The methodof claim 11, wherein the thermally responsive hydrogel comprises aplurality of thermoresponsive polymers having a plurality of thickeningtransition temperatures.
 18. A method comprising: introducing atreatment fluid comprising an aqueous base fluid and a thermallyresponsive hydrogel comprising at least one thermoresponsive polymerinto at least a portion of a subterranean formation; allowing the atleast one thermoresponsive polymer to undergo an at least partiallyreversible thickening transition at about, or above, a thickeningtransition temperature; allowing the treatment fluid to at leastpartially solidify in the subterranean formation; allowing thethickening transition of the at least one thermoresponsive polymer to atleast partially reverse about, or below, the thickening transitiontemperature, wherein the at least partially solidified treatment fluidundergoes a solid-to-liquid phase change at about, or below, thethickening transition temperature.
 19. The method of claim 18, whereinthe thickening transition temperature is from about 30° C. to about 210°C.
 20. The method of claim 18, wherein a viscosity of the treatmentfluid increases to a viscosity from about 2 cP to about 250 cP at aboutor above the thickening transition temperature.